Sterling: New reverse osmosis treatment plant to be online by late summer

Some unexpected hang-ups have pushed back the time before residents receive the full benefits of the new water treatment plant until late summer. The plant has been filtering the city’s water since November, but the full 80/20 reverse osmosis (RO)-filtered water to regular filtered water mix will eke its way into Sterling’s system over the next several months…

The water treatment plant will significantly lower uranium and pollutant levels, and significantly drop the hardness of the water.

Most of the issues crews ran into concerned well and distribution issues, but one stood out: A thick, black, non-cohesive material in the well water was clogging up filters faster than expected. “We don’t know entirely what it is,” said Rob Demis, of Hatch Mott MacDonald, the company overseeing construction of the plant. He brought a bottle of it to show the council, showing it as fine black sediment layered at the bottom of clear ground water. After a couple of shakes, the water turned black and opaque. The material – 20 percent organic material and 30 percent manganese, with traces of other elements, such as iron and silicon – is also odorless, though Demis guessed it would have tasted “metallic” and “bitter.” The manganese gives the material its color.

The raw water filter running now, which catches sediment down to the one-micron level, has caught the material at the five-micron level. Crews would change the filters every couple of days in November, but it’s since become less prevalent, which Demis credited to the city’s aggressive pipe flushing program. “We don’t know the origin. It may be coming out of the pipes. It may be coming out of the formations,” he said. “The good news now is we’re filtering it.”

The plant also encountered issues with its distribution system, which wasn’t getting water out of the plant quick enough to the city’s distribution tanks to fill them. Demis said the plant quickly fills Sterling’s north and south tanks but doesn’t reach its west tank. Part of the problem might be buildup in the pipes over the years slowing water flow (like plaque clogging an artery, Demis said), but many of the pipes are also 100 years old…

The plant had planned on having the ability to pump more than 7,900 gallons of water per minute, but right now it can only pump about 5,500. That means that of the treatment plant’s three pump levels – the third allowing the maximum amount of water to pump during peak use – they can only pump enough water to fulfill the first two…

Water treatment crews have also been finishing construction on two deep water injection wells, which will deposit treated waste water more than a mile underground. One of the wells was dug at about 7,200 feet underground, as recommended by EPA estimates, while the second was dug to about 6,100 feet.

Demis said the area’s geology hasn’t been fully explored, so the crew will need to test the area over time.